Error: “invalid use of incomplete type ‘RSA {aka struct rsa_st}” in OpenSSL 1.1.0

Question

I have old code that was written to link against an old version of openssl. Part of this code loads a key from a PEM file, and tries to understand whether this key is a priv

Answer 1

After 1.1.1 OpenSSL Supports getter what return each parameter like this.

const BIGNUM *RSA_get0_n(const RSA *d);
const BIGNUM *RSA_get0_e(const RSA *d);
const BIGNUM *RSA_get0_d(const RSA *d);
const BIGNUM *RSA_get0_p(const RSA *d);
const BIGNUM *RSA_get0_q(const RSA *d);
const BIGNUM *RSA_get0_dmp1(const RSA *r);
const BIGNUM *RSA_get0_dmq1(const RSA *r);
const BIGNUM *RSA_get0_iqmp(const RSA *r);

So if you don't need to considerate below version of OpenSSL less than 1.1.1 these code will make simple code. AND other structures support kind of this getter too. You can find more information of functions this. https://www.openssl.org/docs/man1.1.1/man3/